An even more recent study has failed to replicate the glucose effect entirely, too: Lange, F., & Eggert, F. (2014). Sweet delusion. Glucose drinks fail to counteract ego depletion. Appetite, 75, 54-63 <-- This one also has an interesting survey of the methodological flaws in similar studies.

Also, there's some evidence (still preliminary) that ego depletion effects decline with age: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0026351 <-- free access paper if anyone wants to read it. It basically looks at a meta-analysis by Hagger done about 2010? I think, and shows a significantly higher effect for younger people (which, being psyc and reliant on college students most of the time, is most of them) - then conducted their own study and found the same (using groups of <25 vs. 40-65). Since 25 is approximately when the pre-frontal cortex is fully finished maturing, maybe the effect has something to do with that.

Also, in terms of the 'out of willpower' and giving up thing... several studies have shown that with sufficient incentive (money, being told the research will help develop Alzheimer's therapies) the ego depletion effect goes away (but then comes back triple-fold on a third non-motivated task). Also, people tend to conserve willpower when they expect to need it later. So you don't have to give up, it might just be a bit harder - but if a few dollars (literally what it was) can motivate someone out of it then you can probably motivate yourself out of it for anything important. This is where the muscle analogy comes into play, like an athlete resting for a big match then pushing through discomfort during it.

^Ref for the last paragraph: Muraven, M., Slessareva, E. (2003). Mechanisms of Self-Control Failure: Motivation and Limited Resources. Personality and Social Psychology Bulletin, 29(7), 894-906

All in all, I'm not convinced one of those things is going on, because there's no explanation there as to why they would happen more for a task that requires self-control than one that doesn't. Most ego-depletion studies match up tasks to make them the same domain, often the same length and tediousness. Why would a task requiring more self-control give you more physical discomfort, hunger, thirst or indignation? The anxiety about willpower depletion I can get behind, but that's only for people who know what they're being tested on.